With in-vehicle devices, such as a transmission, an air conditioner, and so on, being highly advanced, a large number of electronic control units constituting a conventional vehicle control system have been installed in a vehicle. These electronic control units, referred to simply as ECUs, are distributedly located to individually control corresponding predetermined target devices included in the in-vehicle devices.
A various types of sensors have been installed in the vehicle for measuring (monitoring) physical properties associated with the in-vehicle devices; these physical properties are required for ECUs to control the in-vehicle devises.
For example, if first and second ECUs designed to control first and second in-vehicle devices as targets, respectively, the first ECU is electrically connected to a first sensor for measuring a physical property associated with the first target device. Similarly, the second ECU is electrically connected to a second sensor for measuring a physical property associated with the second target device.
When the physical properties are input, as first and second pieces of sensor information (monitor information), from the first and second sensors to the first and second ECUs, respectively, the first and second ECUs are configured to individually control the first and second in-vehicle devices based on the first and second pieces of sensor information, respectively.
In such a conventional vehicle control system, the ECUs are communicatively linked to each other through a CAN (Controller area Network; in other words, CAN bus) as an example of multiplex networks. The CAN allows the ECUs to share, through the multiplex network, pieces of sensor information to be required to the individual controls. An example of the conventional vehicle control systems using the CAN is disclosed in the U.S. Pat. No. 6,711,472 B2 corresponding to Japanese Unexamined Patent Publication No. 2002-206454.
In conventional distributed control systems such as the vehicle control systems, the structure and/or functions of an ECU can be updated in accordance with installability and cost. For example, the wiring configuration of ECUs of a vehicle control system with respect to sensors thereof is changed such that one of two sensors to which an ECU was connected is connected to another ECU. Even if this change is subjected to the vehicle control system, the ECU can indirectly take, via the CAN from another ECU, a piece of sensor information to be required to control a target device associated with the one of the two sensors. This allows the ECU to basically maintain the control function for a target device associated with the one of the two sensors; this control function is substantially equivalent to that of the ECU whose wiring configuration is unchanged.
In such a vehicle control system, if an ECU whose wiring configuration has been changed is designed to control a target device using pieces of sensor information whose measured timings are synchronized with each other (kept in phase with each other), the following significant disadvantage may appear in the vehicle control system. Note that, as such an ECU requiring time-synchronized pieces of sensor information, there is an ECU for controlling intake airflow based on pieces of sensor information synchronously measured respectively by an intake throttle-position sensor and an intake stroke sensor.
Specifically, even though the ECU allows, via the CAN, for sharing of pieces of sensor information obtained by an other ECU to which an intake throttle-position sensor and/or an intake stroke sensor are connected, the obtained timings of the pieces of sensor information may not coincide with each other. This may not ensure the synchronism between the pieces of sensor information.
In this regard, the vehicle control system disclosed in the U.S. Patent Publication No. 6,711,472 B2 cannot solve the disadvantage set forth above because it aims at synchronization between an ECU and sensors connected thereto, and therefore does not focus on synchronism of pieces of sensor information to be obtained from sensors connected to different ECUs, respectively.